package medium;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Set;

/**
 * Created by daodao on 2017/12/4.
 * Problem 15
 * Description: Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0?
 * Find all unique triplets in the array which gives the sum of zero.
 *
 * Note: The solution set must not contain duplicate triplets.
 * For example, given array S = [-1, 0, 1, 2, -1, -4],
 * A solution set is:
 * [
 *  [-1, 0, 1],
 *  [-1, -1, 2]
 * ]
 */
public class ThreeSum {
    public static List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++) {
            if (i == 0 || i > 0 && nums[i] != nums[i - 1]) {
                int sum = 0 - nums[i];
                int low = i + 1;
                int high = nums.length - 1;
                while (low < high) {
                    if (nums[low] + nums[high] == sum) {
                        List<Integer> item = new ArrayList<>();
                        item.add(nums[i]);
                        item.add(nums[low]);
                        item.add(nums[high]);
                        result.add(item);
                        while (low < high && nums[low] == nums[low + 1]) low++;
                        while (low < high && nums[high] == nums[high - 1]) high--;
                        low++;
                        high--;
                    } else if (nums[low] + nums[high] > sum) {
                        high--;
                    } else {
                        low++;
                    }
                }
            }
        }
        return result;
    }
}
